APPARATUS AND METHOD FOR FABRICATING CHIRAL FIBER GRATINGS

An apparatus(100) and method for fabricating fiber gratings from optical fibers(114) by imposing constant or variable chiral refractive index modulation along an optical fiber. The refractive index modulation may be of single helix symmetry or of double helix symmetry. In several embodiments of the present invention the refractive index modulation is imposed by twisting and moving a specially prepared optical fiber through a heater(116) that hea ts a small region of the fiber to a temperature sufficient to allow the fiber t o twist in that region as it moves through the heater. Alternately, a normal optical fiber may specially prepared for use with the apparatus of the prese nt invention at a pre-process stage prior to twisting and heating. In other embodiments of the inventive apparatus, the refractive index modulation is imposed by cutting one or more helical groove patterns into a normal optical fiber, or wrapping a normal fiber with one or more elongated dielectric fibe rs of a smaller diameter than the optical fiber in one or more helical patterns . Advantageously, the fabrication of the chiral fiber grating may be monitored and the fabrication parameters automatically adjusted to ensure that the chiral fiber grating meets desired requirements.